1. Field of the Invention
This invention relates to a back light detecting method, a back light detecting device and an image pick-up camera, in which a back light state is detected according to a subject image.
2. Description of the Related Art
Heretofore, in a video camera, a predetermined brightness is kept by taking feedback in which the brightness of a pick-up picture is detected and a diaphragm is adjusted so that a brightness level of this picture is kept in a predetermined reference level.
In such automatic exposure control, feedback is always effected so that the pick-up picture is to be a reference brightness level set previously. For example, in a picture with a back light in which there is the sun in a background of a subject, feedback in which the brightness level of the whole picture is controlled in low level owing to the sun having a remarkably high brightness level, thus the subject image become dark.
Therefore, in the conventional video camera, a back light state is detected and controlled so that the image becomes not dark more than need and the brightness of a subject image becomes in a medium level in the above state. In such conventional method, as a technique of detecting a back light state, it has been used that a picture is divided into a high brightness region and a low brightness region to detect being in back light when the difference of those brightness levels is large.
By the way, in case of detecting a back light state by using the above method, the back light state is detected only how a picture is divided into a high brightness region and a low brightness region in accordance with a fixed threshold value and those brightness levels are simply compared with each other. Thus more detailed gradation in the area detected having a low brightness and an area of each gradation have not been decision factors for a back light state.
Accordingly, if it is detected that both a small subject and a large background are in the range of low brightness level and the subject is brighter than the background for example, a back light correcting apparatus takes correction so that a brightness level of the background having a larger area and being dark becomes in suitable. As a result, there is a problem that the subject becomes in overexposure and brighter more than need.